I AM NOT A DOCTORSound advice from TomC. Trapped air would very likely result in a pneothroax (lung over expansion injury) aka tear in the lung and very likely a collapsed lung, which in turn would put pressure on the heart and the other lung possibly collapsing it and possibly introduce air bubbles into the blood resulting in the additional complication of embolism. Collapsed lungs do not breathe until intervention occurs (14 gauge needle stabbed into the correct location of the chest), usually from a medical professional or someone with training beyond the normal first aide. In short to say you would be having a bad day would be an understatement.

This is no a small matter and needs to be thoroughly investigated by a dive physician. Active Asthma is a do not dive indicator. See DAN's article http://www.diversalertnetwork.org/medical/faq/faq.aspx?faqid=124

Please keep in mind your dive buddy deserves to know you have active asthma before the dive so they can make their own informed decisions as this affects both of you.